When the temperature outside begins to rise, many people seek the cool comfort of indoor air conditioning. To some people an air conditioner is purely a luxury but to others it's simply a necessity. This guide will discuss the important issues that are relevant when you are considering getting an air conditioner in your home.

Window units
A window air conditioner unit is a complete air conditioner that is simply mounted in the opening of your window. The units are cleverly made small enough to fit into a standard window frame. You close the window down on the unit, plug the unit in and turn it on.
Apart from easy installation and it's small size, a window unit has one important advantage : the condensed water that all air conditioners produce is easy to get rid of. The water will simply drip off the unit outside and can easily be directed elsewhere if a tube is connected.
A typical window air conditioner is rated at 10,000 BTU. (Read more about BTU below)

Split unit systems / central air conditioners
Technically speaking, a split-system air conditioner splits the hot side from the cold side of the system. Instead of having the whole mechanism in the same place like the window unit, the split systems has the condensing unit outside. These systems are larger and are typically used as central air conditioner units. The cool air is generated using the same principle as other air conditioners and it is then sent to the various rooms via a series of ducts.
Central air conditioners typically require a professional installation.

Portable air conditioners
A portable air conditioner is a console unit that can be moved from room to room and other locations. However, they cost a bit more than window units and use more energy, but still, portable units are advantageous to people who just need local cooling or need to move the unit from time to time.
Here you can read more about what a portable air conditioner is and what advantages/disadvantages it has.

BTU guidelines (capacity)
BTU (British Thermal Units) measures the cooling capacity of the air conditioner. The higher the number, the more cooling power the air conditioner has.
A room of 200 square feet will need a 6,500 BTU unit (depending on isolation). Bigger rooms of i.e. 1000 square feet might need up to 18,000 BTU's to cool the room properly. Compare this to the typical cooling capacity of a window unit which is 10,000 BTU. A central unit covering a 2000 square feet house will need a capacity of about 55,000 to 65,000 BTU's.

EER guidelines (efficiency)
EER (energy efficiency rating) is the other important parameter needed to classify air conditioners. The EER number tells you how efficient the air conditioner converts the electrical energy to cool air. For example, if a 10,000-BTU air conditioner consumes 1,000 Watts, its EER is 10 (10,000 BTU/1,000 Watts). So the higher the EER values is the cheaper the unit will be in power consumption.
Although higher EER values are accompanied by higher prices on the air conditioner it is usually a good idea to not compromise. Basically, the more you use your air conditioner the higher the EER value should be. More about this in the section to follow.

Which air conditioner should I buy?
You should buy the unit of the correct capacity and type that has the highest EER, if you can afford it. The guidelines above should give you an idea of what BTU you should aim for. Concerning the EER, you should be careful buying a unit of lower EER because of the attractive lower costs. This will usually result in a false economy as you will end up paying more for your cool air through the electricity bill. Exceptions from this are places such as summerhouses or places where the air conditioner is rarely used as a result of short summers.

In short terms. You should make sure that you are purchasing a unit of high enough capacity (BTU) and high economical efficiency (EER). Be careful that you don't get tempted by cheap units with low EER that actually will result in a high electricity bill making the "cheap" a/c even more expensive than high EER units.

Central Air Conditioner